This invention relates to heat-sensitive cut-off devices for gas conduits and the like, and to a method of manufacturing heat-sensitive cut-offs.
A variety of heat-sensitive cut-off devices have been made to cut-off or stop the flow through a conduit if the temperature rises to a critical level. These devices are typically used on gas supply conduits and the like, in order to stop the flow of gas in the presence of heat or flame. One type of device includes a spring-biased closure member that is temporarily secured from moving to a closed position by soldering. An example of such a device is shown in U.S. Pat. No. 4,290,440. When the melting point of the solder is exceeded the solder melts, freeing the closure member, which can then move to its closed position, stopping the flow through the conduit.
One problem encountered with some of these prior devices is that the solder is exposed to the flow through the conduit, and as the solder melts it is driven or blown by the flow through the conduit to interfere with the operation of the cut-off device. To avoid this problem, the closure member is sometimes secured in a blind hole so that the melting solder is sheltered from the passing gas. However, it is particularly difficult to solder the closure member in a blind hole. The joint must be sufficiently strong to prevent the closure member from inadvertently closing, but it must also readily release when the temperature reaches a critical level. In one manufacturing process, flux is applied to the closure member and to the blind hole in which it is to be mounted, over the appropriate length of the soldered joint. Solder is then applied to the closure member and the closure member is inserted into the blind hole. The assembly is then subjected to a reflow process in a furnace. This is a time consuming process, and the resulting parts are still not completely reliable, and must be tested. A fusible plug could be provided in the bottom of the blind hole to support a spacer that keeps the valve open. When the plug melts the spacer could penetrate into the blind hole, allowing the valve to close. The melted material from the plug would be contained in the blind hole, sheltered from the passing gas, and thus would not interfere with the closing of the valve. However, nothing would prevent the spacer from becoming separated from the blind hole, which could result in misalignment between the spacer and the hole and impair the operation of the valve.